Final answer:
Neandertals were assimilated into modern Homo sapiens through interbreeding, supported by the presence of Neandertal DNA in modern populations and anatomical features in ancient skeletons. DNA studies suggest a complex history of interbreeding and shared ancestry between Neandertals, Denisovans, and modern humans. While beneficial traits may have been acquired through this genetic mixing, it alone does not fully explain Neandertal extinction.
Step-by-step explanation:
Evidence that supports the claim that Neandertals were assimilated into early modern Homo sapiens through interbreeding includes the presence of Neandertal DNA in modern human populations, anatomical features in Late Pleistocene European skeletons, and the discovery of a first-generation offspring of a Neandertal mother and a Denisovan father. Sequencing of Neandertal and Denisovan DNA has shown that these groups were more closely related to each other than to modern humans, suggesting a shared ancestry and a timeline for divergence. Furthermore, modern European and Middle Eastern populations have genetic material indicating 1 to 4 percent of their DNA is of Neandertal origin.
Evidence from nuclear DNA studies indicates interbreeding events replaced the ancient Denisovan Y chromosome with Neandertal Y chromosome variants in some populations. Current research also shows that while some Neandertal genes may have provided beneficial immunities, others potentially increased the risk for certain modern diseases. Despite the absorption of Neandertal DNA, entire Neandertal population extinction was not solely a result of interbreeding, as factors like environmental changes and disease resistance played significant roles.